1. Field of the Invention
This invention relates to an anode assembly for a magnetron used in a microwave oven, which is usually referred to as an electronic range, to generate microwaves for cooking foodstuffs contained in the oven.
2. Description of the Prior Art
Conventional magnetrons are illustrated in FIGS. 1 and 2 of the accompanying drawings. Such conventional magnetrons comprise a direct-heated filament(referred to as a cathode) 1 disposed axially at its central position and an anode cylinder (referred to as an anode) 2 which is an anode structure mounted in a radially outwardly spaced, in surrounding relation to the cathode.
In addition, the magnetron includes a magnetic circuit comprising a magnet 4 (see FIG. 1) and a magnetic pole 5 and provided within a yoke 3 (see FIG. 1) serving as a frame, to apply a magnetic flux into an active space 12 defined between the filament 1 and the anode cylinder 2; an output section comprising an antenna lead 6, an antenna seal 7, an ceramic insulator 8 and an antenna cap 9 (see FIG. 1) for emitting microwave energy transferred from the anode cylinder 2 to the exterior of the magnetron; radiation fins 11 (see FIG. 1) for radiating heat resulting from collision of thermally excited electron with a plurality of vanes 10 disposed radially on the inner periphery of the anode cylinder; and a filter circuit for preventing an unnecessary high frequency component produced in the active space 12 from flowing back to a power source.
When the magnetron thus constructed performs oscillating operation, the thermally excited electron emitted from the filament 1 effect cycloidal movement as they undergo the force of an electric field induced between the vanes 10 and the filament 1 and the magnetic flux applied into the active space 12 between the vanes 10 and the filament 1 and the magnetic flux applied into the active space 12 between the filament and the anode cylinder by the magnetic pole 5 of the magnetic circuit. The thermally excited electron thus accelerated generate the microwave energy which will be received by the vanes 10. The microwave energy transferred to the vanes is emitted through the antenna lead 6 of the output section to the exterior of the magnetron to dielectrically heat and cook the foodstuffs placed within the microwave oven.
The anode cylinder 2 and the anode vanes 10 constituting the anode assembly for the magnetron are made entirely of an expensive material having extremely low impurity content, such as oxygen-free copper. However, use of the expensive oxygen-free copper for making the anode cylinder 2 and the anode vanes 10 causes increase of the cost of the magnetron, while the electrical-grade copper used for the parts results in generation of gas due to a small quantity of the impurities emitted into the active space of the anode assembly. The gas may interfere with the movement of the thermally excited electron, thereby causing abnormal oscillation or a moding phenomenon in which a pattern of the microwave mode in the active space is not maintained constantly.